The invention relates to a battery checker circuit, and more particularly to a circuit which checks the voltage of a storage battery which is used as a drive source in a variety of instruments.
Where a dry cell or a chargeable battery is used as a drive source, it is recognized that the stored energy of the source is gradually dissipated during use, resulting in a decrease in the output voltage of the source. Thus, there must be provided some means for indicating when the battery voltage is reduced below a reference level which is required for the normal and hence safe operation of the associated instrument. While a variety of detection means which detect the battery voltage have been proposed, they are generally complex in arrangement and unstable in operation. It is highly desirable that the battery checker can be constructed in a simple arrangement, using only electrical elements, and provide an accurate indication. Thus it will be convenient if such circuit can be constructed with a combination of the conventional electrical elements in a simple arrangement.
On the other hand, it is known that when a battery checker is constructed incorporating a light emitting display element, there occurs a hysteresis in the illumination versus voltage characteristic of the display element. Specifically, the threshold voltage at which the display element is illuminated during an increasing phase of the battery voltage as when the power switch of an associated instrument is turned on is different from the corresponding level when the battery voltage is decreasing in its value. As a result, there is a difference between the voltage level at which the display element is illuminated and the level at which it is extinguished.